The next step -- generating full-blown lightning strikes -- may come, he said, after the team reprograms their lasers to use more sophisticated pulse sequences that will make longer-lived filaments to further conduct the lightning during storms.

Triggering lightning strikes is an important tool for basic and applied research because it enables researchers to study the mechanisms underlying lightning strikes. Triggered lightning strikes will also allow engineers to evaluate and test the lightning sensitivity of airplanes and critical infrastructure such as power lines.

Although lightning strikes have been the subject of scientific investigation dating back to the 18th century and Benjamin Franklin's kite experiment, they are still not fully understood. Scientists have been able to trigger lightning strikes since the 1970s by shooting small rockets into thunderclouds that spool long wires connected to the ground, but typically only 50 percent of rocket launches actually trigger a lightning strike. The use of laser technology would make the process quicker, more efficient and cost-effective and would be expected to open a number of new applications.

The idea of using lasers to trigger lightning strikes was first suggested more than 30 years ago, but until recently lasers were not powerful enough to generate the long plasma channels needed. The current generation of more powerful pulsed lasers, like the one developed by Kasparian's team, may change that because they can form a large number of plasma filaments -- ionized channels of molecules in the air that act like conducting wires extending into the thundercloud.

The limitation of the experiment, though, was that they could not generate plasma channels that lived long enough to conduct lightning all the way to the ground. The plasma channels dissipated before the lightning could travel more than a few meters along them. The team is currently looking to increase the power of the laser pulses by a factor of 10 and use bursts of pulses to generate the plasmas much more efficiently.

Kasparian conducted the research with his colleagues at CNRS, the University of Lyon, the University of Geneva, École Polytechnique and ENSTA in Palaiseau, France, the Free University of Berlin and the Dresden-Rossendorf Research Center as part of the Teramobile project.

The work was funded jointly by the CNRS, DFG, the French and German ministries of foreign affairs, Agence Nationale de la Recherche, Fonds national suisse de la recherche scientifique, and the Swiss Secrétariat d'État à l'Éducation et à la Recherche.

The paper, "Electric Events Synchronized With Laser Filaments in Thunderclouds," appears in the April 14 issue of Optics Express, the Optical Society of America's (OSA) open-access journal.

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